Paths and straights

This tutorial is based on PHIDL waveguides tutorial

You can create smooth paths in gdsfactory and extrude them with arbitrary cross-sections

Lets create a path:

• Create a blank Path

• Append points to the Path either using the built-in functions (arc(), straight(), euler(), etc) or by providing your own lists of points

• Specify what you want the cross-section (CrossSection) to look like

• Combine the Path and the CrossSection (will output a Device with the path polygons in it)

Path creation

The first step is to generate the list of points we want the path to follow. Let’s start out by creating a blank Path and using the built-in functions to make a few smooth turns.

import gdsfactory as gf
import numpy as np
import matplotlib.pyplot as plt

gf.CONF.plotter = 'holoviews'

P = gf.Path()
P.append(gf.path.arc(radius=10, angle=90))  # Circular arc
P.append(gf.path.straight(length=10))  # Straight section
P.append(gf.path.euler(radius=3, angle=-90))  # Euler bend (aka "racetrack" curve)
P.append(gf.path.straight(length=40))
P.append(gf.path.arc(radius=8, angle=-45))
P.append(gf.path.straight(length=10))
P.append(gf.path.arc(radius=8, angle=45))
P.append(gf.path.straight(length=10))

gf.plot(P)

2022-03-01 18:39:41.709 | INFO     | gdsfactory.config:<module>:52 - Load '/home/runner/work/gdsfactory/gdsfactory/gdsfactory' 4.2.16

p2 = P.copy().rotate()
gf.plot([P, p2])

P.points - p2.points

array([[ 0.00000000e+00,  0.00000000e+00],
       [ 2.59744785e-02, -6.19378670e-02],
       [ 5.24914793e-02, -1.23645416e-01],
       ...,
       [ 3.00861576e+01, -4.76510048e+01],
       [ 3.01066146e+01, -4.77010155e+01],
       [ 3.30355468e+01, -5.47720833e+01]])

We can also modify our Path in the same ways as any other PHIDL object:

• Manipulation with move(), rotate(), mirror(), etc

• Accessing properties like xmin, y, center, bbox, etc

P.movey(10)
P.xmin = 20
gf.plot(P)

We can also check the length of the curve with the length() method:

P.length()

105.3428189759906

Defining the cross-section

Now that we’ve got our path defined, the next step is to tell phidl what we want the cross-section of the path to look like. To do this, we create a blank CrossSection and add whatever cross-sections we want to it. We can then combine the Path and the CrossSection using the gf.path.extrude() function to generate our final geometry:

Option 1: Single layer and width cross-section

The simplest option is to just set the cross-section to be a constant width by passing a number to extrude() like so:

# Extrude the Path and the CrossSection
c = gf.path.extrude(P, layer=(1, 0), width=1.5)
c.plot()

Option 2: Linearly-varying width

A slightly more advanced version is to make the cross-section width vary linearly from start to finish by passing a 2-element list to extrude() like so:

# Extrude the Path and the CrossSection
c = gf.path.extrude(P, layer=(1, 0), widths=(1, 3))
c.plot()

Option 3: Arbitrary Cross-section

You can also extrude an arbitrary cross_section

X = gf.CrossSection()

# Add a a few "sections" to the cross-section
X.add(width=1, offset=0, layer=(1, 0), ports=("in", "out"))
X.add(width=2, offset=2, layer=(2, 0))
X.add(width=2, offset=-2, layer=(2, 0))

c = gf.path.extrude(P, cross_section=X)
c.plot()

Now, what if we want a more complicated straight? For instance, in some photonic applications it’s helpful to have a shallow etch that appears on either side of the straight (often called a trench or sleeve). Additionally, it might be nice to have a Port on either end of the center section so we can snap other geometries to it. Let’s try adding something like that in:

import gdsfactory as gf

p = gf.path.arc()

# Create a blank CrossSection
X = gf.CrossSection()

# Add a a few "sections" to the cross-section
X.add(width=1, offset=0, layer=(1, 0), ports=("in", "out"))
X.add(width=2, offset=2, layer=(2, 0))
X.add(width=2, offset=-2, layer=(2, 0))

# Combine the Path and the CrossSection
straight = gf.path.extrude(p, cross_section=X)

# Quickplot the resulting Component
straight.plot()

Building Paths quickly

You can pass append() lists of path segments. This makes it easy to combine paths very quickly. Below we show 3 examples using this functionality:

Example 1: Assemble a complex path by making a list of Paths and passing it to append()

P = gf.Path()

# Create the basic Path components
left_turn = gf.path.euler(radius=4, angle=90)
right_turn = gf.path.euler(radius=4, angle=-90)
straight = gf.path.straight(length=10)

# Assemble a complex path by making list of Paths and passing it to `append()`
P.append(
    [
        straight,
        left_turn,
        straight,
        right_turn,
        straight,
        straight,
        right_turn,
        left_turn,
        straight,
    ]
)

gf.plot(P)

Example 2: Create an “S-turn” just by making a list of [left_turn, right_turn]

P = gf.Path()

# Create an "S-turn" just by making a list
s_turn = [left_turn, right_turn]

P.append(s_turn)
gf.plot(P)

Example 3: Repeat the S-turn 3 times by nesting our S-turn list in another list

P = gf.Path()

# Create an "S-turn" using a list
s_turn = [left_turn, right_turn]
# Repeat the S-turn 3 times by nesting our S-turn list 3x times in another list
triple_s_turn = [s_turn, s_turn, s_turn]

P.append(triple_s_turn)
gf.plot(P)

Note you can also use the Path() constructor to immediately contruct your Path:

P = gf.Path([straight, left_turn, straight, right_turn, straight])
gf.plot(P)

Waypoint smooth paths

You can also build smooth paths between waypoints with the smooth() function

points = np.array([(20, 10), (40, 10), (20, 40), (50, 40), (50, 20), (70, 20)])
plt.plot(points[:, 0], points[:, 1], ".-")
plt.axis("equal")

(17.5, 72.5, 8.5, 41.5)

import gdsfactory as gf
import numpy as np

points = np.array([(20, 10), (40, 10), (20, 40), (50, 40), (50, 20), (70, 20)])

P = gf.path.smooth(
    points=points,
    radius=2,
    bend=gf.path.euler,  # Alternatively, use pp.arc
    use_eff=False,
)
gf.plot(P)

Waypoint sharp paths

It’s also possible to make more traditional angular paths (e.g. electrical wires) in a few different ways.

Example 1: Using a simple list of points

P = gf.Path([(20, 10), (30, 10), (40, 30), (50, 30), (50, 20), (70, 20)])
gf.plot(P)

Example 2: Using the “turn and move” method, where you manipulate the end angle of the Path so that when you append points to it, they’re in the correct direction. Note: It is crucial that the number of points per straight section is set to 2 (``pp.straight(length, num_pts = 2)``) otherwise the extrusion algorithm will show defects.

P = gf.Path()
P.append(gf.path.straight(length=10, npoints=2))
P.end_angle += 90  # "Turn" 90 deg (left)
P.append(gf.path.straight(length=10, npoints=2))  # "Walk" length of 10
P.end_angle += -135  # "Turn" -135 degrees (right)
P.append(gf.path.straight(length=15, npoints=2))  # "Walk" length of 10
P.end_angle = 0  # Force the direction to be 0 degrees
P.append(gf.path.straight(length=10, npoints=2))  # "Walk" length of 10
gf.plot(P)

import gdsfactory as gf

X = gf.CrossSection()

X.add(width=1, offset=0, layer=(1, 0))
X.add(width=1.5, offset=2.5, layer=(2, 0))
X.add(width=1.5, offset=-2.5, layer=(3, 0))
component = gf.path.extrude(P, X)
component.show()
component.plot()

2022-03-01 18:39:46.425 | INFO     | gdsfactory.show:show:36 - Klayout show extrude_a1b0e5b8: uid 6, ports [], aliases [], 3 polygons, 0 references

Custom curves

Now let’s have some fun and try to make a loop-de-loop structure with parallel straights and several Ports.

To create a new type of curve we simply make a function that produces an array of points. The best way to do that is to create a function which allows you to specify a large number of points along that curve – in the case below, the looploop() function outputs 1000 points along a looping path. Later, if we want reduce the number of points in our geometry we can trivially simplify the path.

import numpy as np


def looploop(num_pts=1000):
    """Simple limacon looping curve"""
    t = np.linspace(-np.pi, 0, num_pts)
    r = 20 + 25 * np.sin(t)
    x = r * np.cos(t)
    y = r * np.sin(t)
    points = np.array((x, y)).T
    return points


# Create the path points
P = gf.Path()
P.append(gf.path.arc(radius=10, angle=90))
P.append(gf.path.straight())
P.append(gf.path.arc(radius=5, angle=-90))
P.append(looploop(num_pts=1000))
P.rotate(-45)

# Create the crosssection
X = gf.CrossSection()
X.add(width=0.5, offset=2, layer=1)
X.add(width=0.5, offset=4, layer=2)
X.add(width=1.5, offset=0, layer=3, ports=["in", "out"])
X.add(width=1, offset=0, layer=4)

c = gf.path.extrude(P, X)
c.show()
c.plot()

2022-03-01 18:39:46.696 | INFO     | gdsfactory.show:show:36 - Klayout show extrude_5fa8e0d1: uid 8, ports ['in', 'out'], aliases [], 6 polygons, 0 references

You can create Paths from any array of points – just be sure that they form smooth curves! If we examine our path P we can see that all we’ve simply created a long list of points:

import numpy as np

path_points = P.points  # Curve points are stored as a numpy array in P.points
print(np.shape(path_points))  # The shape of the array is Nx2
print(len(P))  # Equivalently, use len(P) to see how many points are inside

(1359, 2)
1359

Simplifying / reducing point usage

One of the chief concerns of generating smooth curves is that too many points are generated, inflating file sizes and making boolean operations computationally expensive. Fortunately, PHIDL has a fast implementation of the Ramer-Douglas–Peucker algorithm that lets you reduce the number of points in a curve without changing its shape. All that needs to be done is when you made a component component() extruding the path with a cross_section, you specify the simplify argument.

If we specify simplify = 1e-3, the number of points in the line drops from 12,000 to 4,000, and the remaining points form a line that is identical to within 1e-3 distance from the original (for the default 1 micron unit size, this corresponds to 1 nanometer resolution):

# The remaining points form a identical line to within `1e-3` from the original
c = gf.path.extrude(p=P, cross_section=X, simplify=1e-3)
c.plot()

Let’s say we need fewer points. We can increase the simplify tolerance by specifying simplify = 1e-1. This drops the number of points to ~400 points form a line that is identical to within 1e-1 distance from the original:

c = gf.path.extrude(P, cross_section=X, simplify=1e-1)
c.plot()

Taken to absurdity, what happens if we set simplify = 0.3? Once again, the ~200 remaining points form a line that is within 0.3 units from the original – but that line looks pretty bad.

c = gf.path.extrude(P, cross_section=X, simplify=0.3)
c.plot()

Curvature calculation

The Path class has a curvature() method that computes the curvature K of your smooth path (K = 1/(radius of curvature)). This can be helpful for verifying that your curves transition smoothly such as in track-transition curves (also known as “Euler” bends in the photonics world). Euler bends have lower mode-missmatch loss as explained in this paper

Note this curvature is numerically computed so areas where the curvature jumps instantaneously (such as between an arc and a straight segment) will be slightly interpolated, and sudden changes in point density along the curve can cause discontinuities.

import matplotlib.pyplot as plt
import gdsfactory as gf

straight_points = 100

P = gf.Path()
P.append(
    [
        gf.path.straight(
            length=10, npoints=straight_points
        ),  # Should have a curvature of 0
        gf.path.euler(
            radius=3, angle=90, p=0.5, use_eff=False
        ),  # Euler straight-to-bend transition with min. bend radius of 3 (max curvature of 1/3)
        gf.path.straight(
            length=10, npoints=straight_points
        ),  # Should have a curvature of 0
        gf.path.arc(radius=10, angle=90),  # Should have a curvature of 1/10
        gf.path.arc(radius=5, angle=-90),  # Should have a curvature of -1/5
        gf.path.straight(
            length=2, npoints=straight_points
        ),  # Should have a curvature of 0
    ]
)

gf.plot(P)

Arc paths are equivalent to bend_circular and euler paths are equivalent to bend_euler

s, K = P.curvature()
plt.plot(s, K, ".-")
plt.xlabel("Position along curve (arc length)")
plt.ylabel("Curvature")

Text(0, 0.5, 'Curvature')

P = gf.path.euler(radius=3, angle=90, p=1.0, use_eff=False)
P.append(gf.path.euler(radius=3, angle=90, p=0.2, use_eff=False))
P.append(gf.path.euler(radius=3, angle=90, p=0.0, use_eff=False))
gf.plot(P)

s, K = P.curvature()
plt.plot(s, K, ".-")
plt.xlabel("Position along curve (arc length)")
plt.ylabel("Curvature")

Text(0, 0.5, 'Curvature')

You can compare two 90 degrees euler bend with 180 euler bend.

A 180 euler bend is shorter, and has less loss than two 90 degrees euler bend.

import matplotlib.pyplot as plt
import gdsfactory as gf

straight_points = 100

P = gf.Path()
P.append(
    [
        gf.path.euler(radius=3, angle=90, p=1, use_eff=False),
        gf.path.euler(radius=3, angle=90, p=1, use_eff=False),
        gf.path.straight(length=6, npoints=100),
        gf.path.euler(radius=3, angle=180, p=1, use_eff=False),
    ]
)

gf.plot(P)

s, K = P.curvature()
plt.plot(s, K, ".-")
plt.xlabel("Position along curve (arc length)")
plt.ylabel("Curvature")

Text(0, 0.5, 'Curvature')

Transitioning between cross-sections

Often a critical element of building paths is being able to transition between cross-sections. You can use the transition() function to do exactly this: you simply feed it two CrossSections and it will output a new CrossSection that smoothly transitions between the two.

Let’s start off by creating two cross-sections we want to transition between. Note we give all the cross-sectional elements names by specifying the name argument in the add() function – this is important because the transition function will try to match names between the two input cross-sections, and any names not present in both inputs will be skipped.

import numpy as np
import gdsfactory as gf

# Create our first CrossSection
X1 = gf.CrossSection()
X1.add(width=1.2, offset=0, layer=2, name="wg", ports=("o1", "o2"))
X1.add(width=2.2, offset=0, layer=3, name="etch")
X1.add(width=1.1, offset=3, layer=1, name="wg2")

# Create the second CrossSection that we want to transition to
X2 = gf.CrossSection()
X2.add(width=1, offset=0, layer=2, name="wg", ports=("o1", "o2"))
X2.add(width=3.5, offset=0, layer=3, name="etch")
X2.add(width=3, offset=5, layer=1, name="wg2")

# To show the cross-sections, let's create two Paths and
# create Devices by extruding them
P1 = gf.path.straight(length=5)
P2 = gf.path.straight(length=5)
wg1 = gf.path.extrude(P1, X1)
wg2 = gf.path.extrude(P2, X2)

# Place both cross-section Devices and quickplot them
c = gf.Component()
wg1ref = c << wg1
wg2ref = c << wg2
wg2ref.movex(7.5)

c.plot()

Now let’s create the transitional CrossSection by calling transition() with these two CrossSections as input. If we want the width to vary as a smooth sinusoid between the sections, we can set width_type to 'sine' (alternatively we could also use 'linear').

# Create the transitional CrossSection
Xtrans = gf.path.transition(cross_section1=X1, cross_section2=X2, width_type="sine")
# Create a Path for the transitional CrossSection to follow
P3 = gf.path.straight(length=15, npoints=100)
# Use the transitional CrossSection to create a Component
straight_transition = gf.path.extrude(P3, Xtrans)
straight_transition.show()
straight_transition.plot()

2022-03-01 18:39:49.788 | INFO     | gdsfactory.show:show:36 - Klayout show extrude_d74e0984: uid 16, ports ['o1', 'o2'], aliases [], 5 polygons, 0 references

straight_transition.ports["o1"].cross_section.sections

[{'width': <function gdsfactory.path._sinusoidal_transition.<locals>.sine(t)>,
  'offset': <function gdsfactory.path._sinusoidal_transition.<locals>.sine(t)>,
  'layer': 2,
  'ports': ('o1', 'o2'),
  'port_types': ('optical', 'optical'),
  'hidden': False,
  'name': 'wg'},
 {'width': <function gdsfactory.path._sinusoidal_transition.<locals>.sine(t)>,
  'offset': <function gdsfactory.path._sinusoidal_transition.<locals>.sine(t)>,
  'layer': 3,
  'ports': (None, None),
  'port_types': ('optical', 'optical'),
  'hidden': False,
  'name': 'etch'},
 {'width': <function gdsfactory.path._sinusoidal_transition.<locals>.sine(t)>,
  'offset': <function gdsfactory.path._sinusoidal_transition.<locals>.sine(t)>,
  'layer': 1,
  'ports': (None, None),
  'port_types': ('optical', 'optical'),
  'hidden': False,
  'name': 'wg2'}]

straight_transition.ports["o2"].cross_section.sections

[{'width': <function gdsfactory.path._sinusoidal_transition.<locals>.sine(t)>,
  'offset': <function gdsfactory.path._sinusoidal_transition.<locals>.sine(t)>,
  'layer': 2,
  'ports': ('o1', 'o2'),
  'port_types': ('optical', 'optical'),
  'hidden': False,
  'name': 'wg'},
 {'width': <function gdsfactory.path._sinusoidal_transition.<locals>.sine(t)>,
  'offset': <function gdsfactory.path._sinusoidal_transition.<locals>.sine(t)>,
  'layer': 3,
  'ports': (None, None),
  'port_types': ('optical', 'optical'),
  'hidden': False,
  'name': 'etch'},
 {'width': <function gdsfactory.path._sinusoidal_transition.<locals>.sine(t)>,
  'offset': <function gdsfactory.path._sinusoidal_transition.<locals>.sine(t)>,
  'layer': 1,
  'ports': (None, None),
  'port_types': ('optical', 'optical'),
  'hidden': False,
  'name': 'wg2'}]

wg1.plot()

wg2.plot()

Now that we have all of our components, let’s connect() everything and see what it looks like

c = gf.Component('transition_demo')

wg1ref = c << wg1
wgtref = c << straight_transition
wg2ref = c << wg2

wgtref.connect("o1", wg1ref.ports["o2"])
wg2ref.connect("o1", wgtref.ports["o2"])

c.show()
c.plot()

2022-03-01 18:39:50.850 | INFO     | gdsfactory.show:show:36 - Klayout show transition_demo: uid 18, ports [], aliases [], 0 polygons, 3 references

Note that since transition() outputs a CrossSection, we can make the transition follow an arbitrary path:

# Transition along a curving Path
P4 = gf.path.euler(radius=25, angle=45, p=0.5, use_eff=False)
wg_trans = gf.path.extrude(P4, Xtrans)

c = gf.Component()
wg1_ref = c << wg1  # First cross-section Component
wg2_ref = c << wg2
wgt_ref = c << wg_trans

wgt_ref.connect("o1", wg1_ref.ports["o2"])
wg2_ref.connect("o1", wgt_ref.ports["o2"])

c.plot()

Variable width / offset

In some instances, you may want to vary the width or offset of the path’s cross- section as it travels. This can be accomplished by giving the CrossSection arguments that are functions or lists. Let’s say we wanted a width that varies sinusoidally along the length of the Path. To do this, we need to make a width function that is parameterized from 0 to 1: for an example function my_width_fun(t) where the width at t==0 is the width at the beginning of the Path and the width at t==1 is the width at the end.

def my_custom_width_fun(t):
    # Note: Custom width/offset functions MUST be vectorizable--you must be able
    # to call them with an array input like my_custom_width_fun([0, 0.1, 0.2, 0.3, 0.4])
    num_periods = 5
    w = 3 + np.cos(2 * np.pi * t * num_periods)
    return w


# Create the Path
P = gf.path.straight(length=40)

# Create two cross-sections: one fixed width, one modulated by my_custom_offset_fun
X = gf.CrossSection()
X.add(width=3, offset=-6, layer=(2, 0))
X.add(width=my_custom_width_fun, offset=0, layer=(1, 0))

# Extrude the Path to create the Component
c = gf.path.extrude(P, cross_section=X)
c.plot()

We can do the same thing with the offset argument:

def my_custom_offset_fun(t):
    # Note: Custom width/offset functions MUST be vectorizable--you must be able
    # to call them with an array input like my_custom_offset_fun([0, 0.1, 0.2, 0.3, 0.4])
    num_periods = 3
    w = 3 + np.cos(2 * np.pi * t * num_periods)
    return w


# Create the Path
P = gf.path.straight(length=40)

# Create two cross-sections: one fixed offset, one modulated by my_custom_offset_fun
X = gf.CrossSection()
X.add(width=1, offset=my_custom_offset_fun, layer=(2, 0))
X.add(width=1, offset=0, layer=(1, 0))

# Extrude the Path to create the Component
c = gf.path.extrude(P, cross_section=X)
c.plot()

Offsetting a Path

Sometimes it’s convenient to start with a simple Path and offset the line it follows to suit your needs (without using a custom-offset CrossSection). Here, we start with two copies of simple straight Path and use the offset() function to directly modify each Path.

def my_custom_offset_fun(t):
    # Note: Custom width/offset functions MUST be vectorizable--you must be able
    # to call them with an array input like my_custom_offset_fun([0, 0.1, 0.2, 0.3, 0.4])
    num_periods = 1
    w = 2 + np.cos(2 * np.pi * t * num_periods)
    return w


P1 = gf.path.straight(length=40)
P2 = P1.copy()  # Make a copy of the Path

P1.offset(offset=my_custom_offset_fun)
P2.offset(offset=my_custom_offset_fun)
P2.mirror((1, 0))  # reflect across X-axis

gf.plot([P1, P2])

Modifying a CrossSection

In case you need to modify the CrossSection, it can be done simply by specifying a name argument for the cross-sectional element you want to modify later. Here is an example where we name one of thee cross-sectional elements 'myelement1' and 'myelement2':

# Create the Path
P = gf.path.arc(radius=10, angle=45)

# Create two cross-sections: one fixed width, one modulated by my_custom_offset_fun
X = gf.CrossSection()
X.add(width=1, offset=0, layer=(1,0), ports=("o1", "o2"), name="myelement1")
X.add(width=1, offset=3, layer=(2,0), name="myelement2")

c = gf.path.extrude(P, X)
c.plot()

In case we want to change any of the CrossSection elements, we simply access the Python dictionary that specifies that element and modify the values

# Copy our original CrossSection
Xcopy = X.copy()

# Modify
Xcopy["myelement2"]["width"] = 2  # X['myelement2'] is a dictionary
Xcopy["myelement2"]["layer"] = 1  # X['myelement2'] is a dictionary

# Extrude the Path to create the Device
c = gf.path.extrude(P, cross_section=Xcopy)
c.plot()

import gdsfactory as gf

X1 = gf.CrossSection()
X1.add(width=1.2, offset=0, layer=2, name="wg", ports=("o1", "o2"))
X1.add(width=2.2, offset=0, layer=3, name="etch")
X1.add(width=1.1, offset=3, layer=1, name="wg2")

# Create the second CrossSection that we want to transition to
X2 = gf.CrossSection()
X2.add(width=1, offset=0, layer=2, name="wg", ports=("o1", "o2"))
X2.add(width=3.5, offset=0, layer=3, name="etch")
X2.add(width=3, offset=5, layer=1, name="wg2")

Xtrans = gf.path.transition(cross_section1=X1, cross_section2=X2, width_type="sine")


P1 = gf.path.straight(length=5)
P2 = gf.path.straight(length=5)
wg1 = gf.path.extrude(P1, X1)
wg2 = gf.path.extrude(P2, X2)

P4 = gf.path.euler(radius=25, angle=45, p=0.5, use_eff=False)
wg_trans = gf.path.extrude(P4, Xtrans)
# WG_trans = P4.extrude(Xtrans)


c = gf.Component()
wg1_ref = c << wg1
wg2_ref = c << wg2
wgt_ref = c << wg_trans

wgt_ref.connect("o1", wg1_ref.ports["o2"])
wg2_ref.connect("o1", wgt_ref.ports["o2"])

c.plot()

len(c.references)

3

Note

Any unamed section in the CrossSection won’t be transitioned.

If you don’t add any named sections in a cross-section it will give you an error when making a transition

import gdsfactory as gf
import numpy as np

P = gf.Path()
P.append(gf.path.arc(radius=10, angle=90))  # Circular arc
P.append(gf.path.straight(length=10))  # Straight section
P.append(gf.path.euler(radius=3, angle=-90))  # Euler bend (aka "racetrack" curve)
P.append(gf.path.straight(length=40))
P.append(gf.path.arc(radius=8, angle=-45))
P.append(gf.path.straight(length=10))
P.append(gf.path.arc(radius=8, angle=45))
P.append(gf.path.straight(length=10))

gf.plot(P)

X = gf.CrossSection()
X.add(width=1, offset=0, layer=(2,0))
c = gf.path.extrude(P, X)
c.plot()

X2 = gf.CrossSection()
X2.add(width=2, offset=0, layer=(2,0))
c = gf.path.extrude(P, X2)
c.plot()

For example this will give you an error

T = gf.path.transition(X, X2)

Solution

P = gf.path.straight(length=10, npoints=101)

X = gf.CrossSection()
X.add(width=1, offset=0, layer=gf.LAYER.WG, name="core", ports=("o1", "o2"))
X.add(width=3, offset=0, layer=gf.LAYER.SLAB90)
c = gf.path.extrude(P, X)
c.plot()

X2 = gf.CrossSection()
X2.add(width=3, offset=0, layer=gf.LAYER.WG, name="core", ports=("o1", "o2"))
c2 = gf.path.extrude(P, X2)
c2.plot()

T = gf.path.transition(X, X2)
c3 = gf.path.extrude(P, T)
c3.plot()

c4 = gf.Component()

start_ref = c4 << c
trans_ref = c4 << c3
end_ref = c4 << c2

trans_ref.connect("o1", start_ref.ports["o2"])
end_ref.connect("o1", trans_ref.ports["o2"])

DeviceReference (parent Device "extrude_134e6fc7", ports ['o1', 'o2'], origin [20.  0.], rotation 0, x_reflection False)

c4.plot()

cross-section

You can create functions that return a cross_section in 2 ways:

• gf.partial can customize an existing cross-section for example gf.cross_section.strip

• define a function that returns a cross_section

import gdsfactory as gf
from gdsfactory.tech import Section

pin = gf.partial(
    gf.cross_section.strip,
    layer=(2, 0),
    sections=(
        Section(layer=gf.LAYER.P, width=2, offset=+2),
        Section(layer=gf.LAYER.N, width=2, offset=-2),
    ),
)

c = gf.components.straight(cross_section=pin)
c.plot()

pin10 = gf.components.straight(cross_section=pin, length=10)
pin10.plot()

finally, you can also pass most components Dict that define the cross-section

gf.components.straight(
    layer=(1, 0),
    width=0.5,
    sections=(
        Section(layer=gf.LAYER.P, width=1, offset=+2),
        Section(layer=gf.LAYER.N, width=1, offset=-2),
    ),
)

2022-03-01 18:39:55.343 | INFO     | gdsfactory.show:show:36 - Klayout show straight_ff974c9e: uid 35, ports ['o1', 'o2'], aliases [], 3 polygons, 0 references

straight_ff974c9e: uid 35, ports ['o1', 'o2'], aliases [], 3 polygons, 0 references

straight_ff974c9e: uid 35, ports ['o1', 'o2'], aliases [], 3 polygons, 0 references

import numpy as np
import gdsfactory as gf

# Create our first CrossSection
X1 = gf.CrossSection()
X1.add(width=0.5, offset=0, layer=1, name="wg", ports=("o1", "o2"))
X1.add(width=0.2, offset=0, layer=3, name="slab")

# Create the second CrossSection that we want to transition to
X2 = gf.CrossSection()
X2.add(width=0.5, offset=0, layer=1, name="wg", ports=("o1", "o2"))
X2.add(width=3.0, offset=0, layer=3, name="slab")

# To show the cross-sections, let's create two Paths and
# create Devices by extruding them
P1 = gf.path.straight(length=5)
P2 = gf.path.straight(length=5)
wg1 = gf.path.extrude(P1, X1)
wg2 = gf.path.extrude(P2, X2)

# Place both cross-section Devices and quickplot them
c = gf.Component()
wg1ref = c << wg1
wg2ref = c << wg2
wg2ref.movex(7.5)

# Create the transitional CrossSection
Xtrans = gf.path.transition(cross_section1=X1, cross_section2=X2, width_type="linear")
# Create a Path for the transitional CrossSection to follow
P3 = gf.path.straight(length=15, npoints=100)
# Use the transitional CrossSection to create a Component
straight_transition = gf.path.extrude(P3, Xtrans)
straight_transition.plot()

s = gf.export.to_3d(straight_transition, layer_set=gf.layers.LAYER_SET)
s.show()

/usr/share/miniconda/envs/anaconda-client-env/lib/python3.9/site-packages/IPython/core/display.py:419: UserWarning: Consider using IPython.display.IFrame instead
  warnings.warn("Consider using IPython.display.IFrame instead")